In recent years, practical application of a TPMS (tire pressure monitoring system) has attracted a lot of attention as car electronics technology for guaranteeing safety and comfort of an automobile with regard to the tires. TPMSs can be roughly classified into a direct measurement type that directly measures the air pressure in each tire and an indirect measurement type that detects insufficient air pressure from the rotation speed difference of two wheels.
FIGS. 9-11 show a conventional typical direct measurement type TPMS.
The TPMS shown in FIG. 9 has receiving antennas 104A, 104B, 104C, 104D with relatively low sensitivity arranged in wheel housings or at other places close to tires 102FL, 102FR, 102RL, 102RR installed on automobile 100. Each of receiving antennas 104A-104D is connected to receiver 106 via respective power supply lines. Tires 102FL, 102FR, 102RL, 102RR are equipped with various kinds of sensors used for detecting air pressure, temperature, etc., of the corresponding tires and sensor modules 108A, 108B, 108C, 108D having transmitters, etc., that transmit the data of the sensor measurement results through radio waves with a certain frequency (such as 315 MHz), respectively. When receiver 106 selects the radio waves input from one of receiving antennas 104A-104D, the sensor module 108 corresponding to or close to that receiving antenna 104 is selected, and the tire state information (air pressure measurement value, temperature measurement value, etc.) sent through a wireless RF signal from said sensor module 108 is input and demodulated. If the measurement value is outside an allowed range, it means that the corresponding tire 102 has a problem or is abnormal, and a warning will be sent through display 110 in the automobile.
The TPMS shown in FIG. 10 has starting antennas 110A, 110B, 11C, 110D arranged close to tires 102FL, 102FR, 102RL, 102RR, respectively, and has only one receiving antenna 104. Each of said starting antennas 110A-110D and receiving antenna 104 are connected to receiver 106 via respective power supply lines. Receiver 106 operates starting antenna 110 close to selected tire 102 in order to monitor the state of each of tires 102FL-102RR. A start signal or request signal with a low frequency (for example, 125 kHz) is supplied to the sensor module 108 of that tire 102 using the electromagnetic induction method, and the tire state information transmitted wirelessly (RF signal) from the corresponding sensor module 108 is input corresponding to said request signal.
The TPMS shown in FIG. 11 does not have antennas arranged close to tires 102FL, 102FR, 102RL, 102RR and has only one receiving antenna 104. In this case, however, ID information transmitted together with the tire state information from the sensor module 108 of each tire 102 is set and registered in receiver 106 in relation to the installation position of the corresponding tire 102. Receiver 106 demodulates the radio waves received by receiving antenna 104 and reads the ID. In this way, it is possible to determine the wheel position where tire 102 is installed as the radio wave transmitter based on the set registration information.
For the aforementioned conventional direct measurement type TPMSs, there are problems in configuration or use with regard to the function of identifying the installation position of each tire as a radio wave transmitter. That is, for TPMSs shown in FIGS. 9 and 10, since receiving antennas 104A, 104B, 104C, 104D or starting antennas 110A, 110B, 110C, 110D are arranged close to tires 102FL, 102RL, 102RL, 102RR, respectively, the number of parts is increased, and the configuration of the entire device is complicated. The cost of the device is also increased. The TPMS shown in FIG. 11 has a simple configuration since the number of parts is reduced. However, every time a tire on a wheel is replaced, it is necessary to set and register the installation wheel position of the newly installed tire corresponding to the ID information in receiver 106. The work required for application is a bottleneck.
An object of the present invention is to solve the problems of the aforementioned conventional technology by providing a tire monitoring device and a tire problem detecting device, which have a simple configuration and compact size, require no special means or operation during operation, and can accurately identify the wheel position where each tire as a radio wave transmitter is installed.